Vapor phase growth method

ABSTRACT

Provided is a vapor phase growth method according to an embodiment including loading a first substrate into a reaction chamber, generating a first mixed gas by mixing an indium containing gas, an aluminum containing gas, and a nitrogen compound containing gas, and forming a first indium aluminum nitride film on the first substrate by supplying the first mixed gas into the reaction chamber, the first substrate being rotated at a first rotation speed of 300 rpm or more.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Applications No. 2018-036381, filed on Mar. 1, 2018, theentire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a vapor phase growth method ofsupplying a gas to form a film on a substrate.

BACKGROUND OF THE INVENTION

A high electron mobility transistor (HEMT) using GaN based semiconductorrealizes a high breakdown voltage and low ON resistance. In the HEMT, atwo-dimensional electron gas (2 DEG) induced in a heterointerfacebetween a channel layer and a barrier layer stacked is used as a currentpath.

For example, gallium nitride (hereinafter, also referred to as GaN) isused for the channel layer, and aluminum gallium nitride (hereinafter,also referred to as AlGaN) is used for the barrier layer. It has beenstudied to apply indium aluminum nitride (hereinafter, also referred toas InAlN) instead of the aluminum gallium nitride for the barrier layer.

Since the InAlN has large spontaneous polarization, the 2 DEGconcentration at the interface between the InAlN and the GaN can beincreased. Therefore, the HEMT with low ON resistance can be realized.In addition, lattice matching with the GaN can be realized by settingthe In composition in the InAlN (In/(In+Al)) to about 17 atom %.Therefore, distortion due to lattice mismatching disappears, and thus,the reliability of the HEMT improves.

In addition, the stacked structure of the InAlN film and the GaN film isexpected to be applied to a dielectric mirror used for a surfaceemitting laser or the like. With respect to the application to theabove-mentioned dielectric mirror, it is required that the interfacebetween the GaN film and the InAlN film is abrupt, that is, thecomposition of the compound of the above two films sharply changes.

However, in the vapor phase growth of the InAlN film, unintentional Gaincorporation into the InAlN film is a problem. If the gallium isincorporated into the InAlN film, for example, there is a concern thatthe 2 DEG density at the interface between the InAlN and the GaNdecreases and the electron mobility decreases. In addition, since sharpchanges in the composition of the compound cannot be obtained, it isdifficult to form a good dielectric mirror.

As a cause of the occurrence of unintentional Ga incorporation into theInAlN film, it is considered that deposits containing Ga are generatedin the upstream portion of the growth apparatus during the growth of thefilm containing Ga performed before the growth of the InAlN film, Ga isejected into the growth atmosphere during the growth of the InAlN filmfrom the deposits containing Ga, and the Ga is incorporated into theInAlN film.

J. Lu et al., MRS Advances, 2017.174, pp 329, discloses an InAlN filmwhich is formed using an apparatus for supplying a separation gas asillustrated in FIG. 1(b) of J. Lu et al. and in which unintentionalgallium incorporation is suppressed.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a vapor phasegrowth method including: loading a first substrate into a reactionchamber; generating a first mixed gas by mixing an indium containinggas, an aluminum containing gas, and a nitrogen compound containing gas;and forming a first indium aluminum nitride film on the first substrateby supplying the first mixed gas into the reaction chamber, the firstsubstrate being rotated at a first rotation speed of 300 rpm or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a vapor phase growth apparatusused in a vapor phase growth method according to a first embodiment.

FIG. 2 is a view illustrating process steps of the vapor phase growthmethod according to the first embodiment.

FIG. 3 is an explanatory diagram of effects of the vapor phase growthmethod according to the first embodiment.

FIG. 4 is a view illustrating process steps of a vapor phase growthmethod according to a second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to the drawings.

In this specification, in some cases, the same or similar components aredenoted by the same reference numerals.

In this specification, the direction of gravity in a state where thevapor phase growth apparatus is installed so as to be capable of forminga film is defined as “down”, and the opposite direction is defined as“up”. Therefore, “below” denotes a position in the direction of gravitywith respect to the reference, “downward” denotes the direction ofgravity with respect to the reference. In addition, “above” denotes aposition in the direction opposite to the gravity direction with respectto the reference, and “upward” denotes the direction opposite to thegravity direction with respect to the reference. In addition, “verticaldirection” is the direction of gravity.

In addition, in this specification, “process gas” is a generic name ofgases used for forming a film on a substrate and is a concept including,for example, a source gas, a carrier gas, a dilution gas, and the like.

First Embodiment

A vapor phase growth method according to a first embodiment includesloading a first substrate into a reaction chamber; generating a firstmixed gas by mixing an indium containing gas, an aluminum containinggas, and a nitrogen compound containing gas; and forming a first indiumaluminum nitride film on the first substrate by supplying the firstmixed gas into the reaction chamber, the first substrate being rotatedat a first rotation speed of 300 rpm or more. Furthermore, the vaporphase growth method includes generating a second mixed gas by mixing atleast a gallium containing gas and the nitrogen-compound containing gas;and forming a first gallium-containing nitride film on the firstsubstrate by supplying the second mixed gas into the reaction chamber,the first substrate being rotated at a second rotation speed of 300 rpmor more. The forming the first indium aluminum nitride film iscontinuously conducted without unloading the first substrate from thereaction chamber after the forming the first gallium-containing nitridefilm.

FIG. 1 is a schematic cross-sectional view of a vapor phase growthapparatus used in the vapor phase growth method according to the firstembodiment. The vapor phase growth apparatus according to the firstembodiment is, for example, a single wafer type epitaxial growthapparatus using metal organic chemical vapor deposition (MOCVD).

The vapor phase growth apparatus according to the first embodimentincludes a reaction chamber 10, a first gas supply path 11, a second gassupply path 12, and a third gas supply path 13. The reaction chamber 10includes a holder 15, a rotator unit 16, a rotation shaft 18, a rotationdriving mechanism 19, a gas supply port 20, a mixed gas chamber 21, ashower plate 22, an in-heater 24, an out-heater 26, a reflector 28, asupport column 34, a fixed base 36, a fixed shaft 38, and a gasdischarge port 40.

The first gas supply path 11, the second gas supply path 12, and thethird gas supply path 13 are connected to the gas supply port 20 andsupply the process gas to the mixed gas chamber 21.

The first gas supply path 11 supplies, for example, a first process gascontaining an organic metal of a group III element and a carrier gas tothe reaction chamber 10. A plurality of the first gas supply paths 11can be provided. In addition, the plurality of first gas supply paths 11may be unified. The first process gas is a gas containing a group IIIelement for forming a group III-V semiconductor film on a wafer.

The Group III elements are, for example, gallium (Ga), aluminum (Al),indium (In). In addition, the organic metal is, for example, trimethylgallium (TMG), trimethyl aluminum (TMA), trimethyl indium (TMI).

The second gas supply path 12 supplies a second process gas containing anitrogen compound as a source of nitrogen (N) to the reaction chamber10. The nitrogen compound is, for example, ammonia (NH₃). The secondprocess gas is a source gas of a group V element for forming a groupIII-V semiconductor film on a wafer. The group V element is nitrogen(N).

In addition, the nitrogen compound may be an active nitrogen compound.But not limited to ammonia, a gas containing other nitrogen compoundssuch as hydrazine, alkylhydrazine, alkylamine and the like may be used.

The third gas supply path 13 supplies, for example, a third process gasas a dilution gas for diluting the first process gas and the secondprocess gas to the reaction chamber 10. By diluting the first processgas and the second process gas with the dilution gas, the concentrationsof the group III element and the group V element supplied to thereaction chamber 10 are adjusted. The dilution gas is, for example, ahydrogen gas, a nitrogen gas, an inert gas such as an argon gas or amixed gas thereof.

The first gas supply path 11, the second gas supply path 12, and thethird gas supply path 13 join in front of the gas supply port 20.Therefore, the first process gas, the second process gas, and the thirdprocess gas are mixed in front of the gas supply port 20 to become amixed gas. The mixed gas of the first process gas, the second processgas, and the third process gas is supplied from the gas supply port 20to the mixed gas chamber 21.

In addition, the mixing of the process gases is not always necessarilyperformed in the pipe on the upstream side of the mixed gas chamber 21.Several process gas pipes may be individually connected to the mixed gaschamber 21, and the mixing of the process gases may be performed in themixed gas chamber 21.

By mixing the process gas and ejecting the mixed process gas from theshower plate 22 to the reaction chamber 10, the flow rate and thedensity of the gas ejected from each gas ejection hole are maintaineduniform, so that the gas flow inside the reaction chamber 10 tends tobecome a laminar flow. For this reason, it is considered that substancesadhering to the surface of the shower plate 22 are unlikely to begenerated.

The reaction chamber 10 is provided with, for example, a cylindricalwall surface 17 made of stainless steel. The shower plate 22 is providedabove the reaction chamber 10. The shower plate 22 is provided betweenthe reaction chamber 10 and the mixed gas chamber 21.

The shower plate 22 is provided with a plurality of gas ejection holes.The mixed gas of the process gas is supplied into the reaction chamber10 from the mixed gas chamber 21 through a plurality of gas ejectionholes.

Furthermore, the surface of the wafer Wand the shower plate 22 areseparated by 3 cm or more from each other. Since the interval betweenthe surface of the wafer W and the shower plate 22 is wide, the processgas that has reached the surface of the wafer W hardly returns to theshower plate 22 side again, and the reaction products are prevented fromadhering to the surface of the shower plate 22. In other words, sincethe interval between the surface of the wafer W and the shower plate 22is wide, a turbulent flow is unlikely to be generated between thesurface of the wafer W and the shower plate 22, and adhesion of reactionproducts to the surface of the shower plate 22 is suppressed.

Since reaction products are unlikely to adhere to the surface of theshower plate 22 facing the surface of the wafer W, unintentional Gaincorporation into the InAlN film is suppressed. In addition, surfacedefects caused by falling of the reaction products adhering to theshower plate 22 onto the surface of the wafer Ware unlikely to begenerated. Therefore, a high-quality film with low defect density isformed.

The distance between the surface of the wafer Wand the shower plate 22is preferably 3 cm or more and 20 cm or less, more preferably 5 cm ormore and 15 cm or less. If the distance is below the above-mentionedrange, there is a concern that the process gas that has reached thesurface of the wafer W returns to the shower plate 22 side again, andreaction products may adhere to the surface of the shower plate 22. Inaddition, if the distance exceeds the above-mentioned range, thermalconvection occurs inside the reaction chamber 10, and thus, there is aconcern that the uniformity of the film thickness and the uniformity ofthe film quality of the film 50 formed on the surface of the wafer W maydecrease.

In addition, with respect to the gas ejection holes provided on thesurface of the shower plate 22, the interval between the closestejection holes is preferably 1 mm or more and 15 mm or less. Theinterval is more preferably 3 mm or more and 10 mm or less. In addition,in some cases, unevenness may be provided on the gas ejection surface ofthe shower plate to stabilize the gas flow ejected from the shower plate22. However, if the unevenness becomes too large, the reaction productadheres to the surface of the shower plate 22, which is not preferable.The preferable unevenness on the surface of the shower plate 22 is suchthat the angle between the surface of the uneven portion and thehorizontal direction is 45 degrees or less. The angle is more preferably30 degrees or less, and most preferably 20 degrees or less.

In addition, the height difference (the difference of distance in thevertical direction between the uppermost portion and the lowermostportion) of the gas ejection hole on the gas ejection surface of theshower plate 22 is preferably 15 mm or less. The height difference ismore preferably 10 mm or less, and most preferably 5 mm or less. In acase where the height difference is larger than these values, depositsare generated on the surface of the shower plate 22, and thus, thesurface defect concentration increases at the time of film formation.

The holder 15 is provided inside the reaction chamber 10. On the holder15, a wafer W as an example of a substrate can be mounted. The holder 15is, for example, in a ring shape. The holder 15 is provided with anopening at the center thereof. Such a ring-shaped holder 15 can be usedwhen an opaque substrate such as a Si substrate is used, and highin-plane uniformity can be obtained. In addition, the shape of theholder 15 may be a substantially flat plate shape having no cavity atthe center thereof.

The holder 15 is formed by using, for example, ceramics such as siliconcarbide (SiC), tantalum carbide (TaC), boron nitride (BN), or pyrolyticgraphite (PG) or carbon as a base material. As the holder 15, forexample, carbon coated with SiC, BN, TaC, PG, or the like can be used.

The holder 15 is fixed to the upper portion of the rotator unit 16. Therotator unit 16 is fixed to the rotation shaft 18. The holder 15 isindirectly fixed to the rotation shaft 18.

The rotation shaft 18 is rotatable by the rotation driving mechanism 19.It is possible to rotate the holder 15 by rotating the rotation shaft bythe rotation driving mechanism 19. By rotating the holder 15, it ispossible to self-rotate the wafer W mounted on the holder 15 at a highspeed. The self-rotation denotes that the wafer W rotates about thenormal line passing through the approximate center of the wafer W as therotation axis.

For example, the wafer W is self-rotated at a rotation speed of 300 rpmor more and 3000 rpm or less. The rotation driving mechanism 19 isconfigured with, for example, a motor and a bearing.

The in-heater 24 and the out-heater 26 are provided below the holder 15.The in-heater 24 and the out-heater 26 are provided in the rotator unit16. The out-heater 26 is provided between the in-heater 24 and theholder 15.

The in-heater 24 and the out-heater 26 heat the wafer W held by theholder 15. The in-heater 24 heats at least the central portion of thewafer W. The out-heater 26 heats the holder 15 and the outer peripheralregion of the wafer W. The in-heater 24 is, for example, in a diskshape. The out-heater 26 is, for example, in a ring shape.

The reflector 28 is provided below the in-heater 24 and the out-heater26. The in-heater 24 and the out-heater 26 are provided between thereflector 28 and the holder 15.

The reflector 28 reflects the heat radiated downward from the in-heater24 and the out-heater 26 so as to improve the heating efficiency of thewafer W. In addition, the reflector 28 prevents members below thereflector 28 from being heated. The reflector 28 is, for example, in adisk shape.

The reflector 28 is made of a material having high heat resistance. Thereflector 28 has heat resistance to a temperature of, for example, 1100°C. or more.

The reflector 28 is formed by using, for example, ceramics such as SiC,TaC, carbon, BN, or PG or a metal such as tungsten as a base material.In the case of using ceramics for the reflector 28, a sintered body or abase material produced by vapor phase growth can be used. As thereflector 28, a carbon base material or the like coated with ceramicssuch as SiC, TaC, BN, PG, or glassy carbon may be used.

The reflector 28 is fixed to the fixed base 36 by, for example, aplurality of the support columns 34. The fixed base 36 is supported by,for example, the fixed shaft 38.

A push-up pin (not illustrated) is provided in the rotator unit 16 inorder to detach the wafer W from the holder 15. The push-up pinpenetrates, for example, the reflector 28 and the in-heater 24.

The gas discharge port 40 is provided at the bottom of the reactionchamber 10. The gas discharge port 40 discharges the surplus reactionproduct after the reaction of the process gas on the surface of thewafer W and the surplus process gas to the outside of the reactionchamber 10.

In addition, a wafer gateway and a gate valve (not illustrated) areprovided to the wall surface 17 of the reaction chamber 10. The wafer Wcan be loaded into the reaction chamber 10 or unloaded from the reactionchamber 10 by the wafer gateway and gate valves.

Next, the vapor phase growth method according to the first embodimentwill be described. In the vapor phase growth method according to thefirst embodiment, an epitaxial growth apparatus illustrated in FIG. 1 isused.

Hereinafter, a case where the indium aluminum nitride film (InAlN film)is continuously formed on the gallium nitride film (GaN film) will bedescribed as an example. For example, the GaN film is used as a channellayer of the HEMT, and the InAlN film is used as a barrier layer of theHEMT. In addition, the band gap of the material of the barrier layer ofthe HEMT is larger than the band gap of the material of the channellayer.

Hereinafter, a case where the channel layer is gallium nitride will bedescribed as an example. However, it is also possible to apply a galliumnitride based film formed based on a mixed gas generated by mixing anindium containing gas and an aluminum containing gas with a gascontaining gallium and a gas containing ammonia for the channel layer.Specifically, the channel layer can be configured with an InGaN film, anAlGaN film, or the like.

FIG. 2 is a view illustrating process steps of the vapor phase growthmethod according to the first embodiment. The vapor phase growth methodaccording to the first embodiment includes a first substrate loadingstep (S100), a first GaN film forming step (S110), a first InAlN filmforming step (S120), a first substrate unloading step (S130), a secondsubstrate loading step (S200), a second GaN film forming step (S210), asecond InAlN film forming step (S220), and a second substrate unloadingstep (S230).

First, the first wafer W (first substrate) is loaded into the reactionchamber 10 (S100). The first wafer W is a silicon substrate of whichsurface is a {111} plane. The error of the plane orientation of thefirst wafer W is preferably 3 degrees or less, and more preferably 2degrees or less. The thickness of the silicon substrate is, for example,700 μm or more and 1.2 mm or less. In addition, the {111} planerepresents a plane crystallographically equivalent to the (111) plane.

Next, the first wafer W is mounted on the holder 15. Next, whileself-rotating the first wafer W by the rotation driving mechanism 19,the first wafer W is heated by the in-heater 24 and the out-heater 26provided below the holder 15.

Next, buffer layers of aluminum nitride (AlN) layer and aluminum galliumnitride (AlGaN) layer are formed on the first wafer W by using TMA, TMG,and ammonia.

Next, a first GaN film is formed on the first wafer W (S110). The firstGaN film is a single crystal. The thickness of the first GaN film is,for example, 100 nm or more and 10 μm or less.

At the time of forming the first GaN film, the first wafer W is rotatedat a predetermined rotation speed (second rotation speed). The secondrotation speed is, for example, 500 rpm or more and 1,500 rpm or less.In addition, the temperature of the first wafer W is, for example,1,000° C. or more and 1,100° C. or less.

At the time of forming the first GaN film, for example, TMG usingnitrogen gas as a carrier gas is supplied from the first gas supply path11. In addition, ammonia is supplied from the second gas supply path 12.In addition, for example, nitrogen gas as a dilution gas is suppliedfrom the third gas supply path 13.

The TMG containing nitrogen gas as a carrier gas, the ammonia, and thenitrogen gas are mixed to generate a mixed gas (second mixed gas), andthe mixed gas is supplied to the mixed gas chamber 21. The mixed gas issupplied from the mixed gas chamber 21 through the shower plate 22 intothe reaction chamber 10.

The mixed gas becomes a laminar flow in a direction substantiallyperpendicular to the surface of the first wafer W in the reactionchamber 10 and is supplied to the surface of the first wafer W. Themixed gas supplied to the surface of the first wafer W flows toward theouter periphery of the first wafer W along the surface of the rotatingfirst wafer W. By a chemical reaction of the mixed gas, the first GaNfilm is formed on the first wafer W.

Next, a first InAlN film is formed on the first wafer W withoutunloading the first wafer W from the reaction chamber 10 (S120). Thefirst InAlN film is a single crystal. The film thickness of the firstInAlN film is, for example, 5 nm or more and 30 nm or less. The filmthickness of the first InAlN film is, for example, smaller than the filmthickness of the first GaN film.

The In composition of the first InAlN film is, for example, about 17atom %. The In composition indicates a ratio of indium occupied to thegroup III element in the first InAlN film.

At the time of forming the first InAlN film, the first wafer W isrotated at a predetermined rotation speed (first rotation speed). Thefirst rotation speed is, for example, 1,600 rpm or more and 1,800 rpm orless. The first rotation speed is, for example, higher than the secondrotation speed. The temperature of the first wafer W is, for example,700° C. or more and 900° C. or less.

At the time of forming the first InAlN film, for example, TMI usingnitrogen gas as a carrier gas is supplied from the first gas supply path11. In addition, for example, TMA using nitrogen gas as a carrier gas issupplied from the first gas supply path 11. In addition, ammonia issupplied from the second gas supply path 12. In addition, for example,nitrogen gas as a dilution gas is supplied from the third gas supplypath 13.

The TMI using nitrogen gas as a carrier gas, the TMA using nitrogen gasas a carrier gas, the ammonia, and the nitrogen gas are mixed togenerate a mixed gas (first mixed gas), and the mixed gas is supplied tothe mixed gas chamber 21. The mixed gas is supplied from the mixed gaschamber 21 through the shower plate 22 into the reaction chamber 10.

The mixed gas becomes a laminar flow in a direction substantiallyperpendicular to the surface of the first wafer W in the reactionchamber 10 and is supplied to the surface of the first wafer W. Themixed gas supplied to the surface of the first wafer W flows toward theouter periphery of the first wafer W along the surface of the rotatingfirst wafer W. By a chemical reaction of the mixed gas, a first InAlNfilm is formed on the first wafer W.

Next, the first wafer W (first substrate) is unloaded from the reactionchamber 10 to the outside (S130).

Next, the second wafer W (second substrate) is loaded into the reactionchamber 10 (S200). After unloading the first wafer W from the reactionchamber 10, the second wafer W is loaded into the reaction chamber 10without performing cleaning (wet cleaning) of the reaction chamber 10.The second wafer W is a silicon substrate similar to the first wafer W.

Next, buffer layers of AlN and AlGaN are formed on the second wafer Wunder the same process conditions as those of the buffer layers formedon the first wafer W.

Next, a second GaN film is formed on the second wafer W (S210). Thesecond GaN film is a single crystal. The second GaN film is formed underthe process conditions similar to those of the first GaN film.

Next, a second InAlN film is formed on the second wafer W withoutunloading the second wafer W from the reaction chamber 10 (S220). Thesecond InAlN film is a single crystal. The second InAlN film is formedunder the process conditions similar to those of the first InAlN film.

At the time of forming the second InAlN film, for example, TMI usingnitrogen gas as a carrier gas is supplied from the first gas supply path11. In addition, for example, TMA using nitrogen gas as a carrier gas issupplied from the first gas supply path 11. In addition, ammonia issupplied from the second gas supply path 12. In addition, for example,nitrogen gas as a dilution gas is supplied from the third gas supplypath 13.

The TMI using nitrogen gas as a carrier gas, the TMA using nitrogen gasas a carrier gas, the ammonia, and the nitrogen gas are mixed togenerate a mixed gas, and the mixed gas is supplied to the mixed gaschamber 21. The mixed gas is supplied from the mixed gas chamber 21through the shower plate 22 into the reaction chamber 10.

The mixed gas becomes a laminar flow in a direction substantiallyperpendicular to the surface of the second wafer W in the reactionchamber 10 and is supplied to the surface of the first wafer W. Themixed gas supplied to the surface of the second wafer W flows toward theouter periphery of the second wafer W along the surface of the rotatingfirst wafer W. By a chemical reaction of the mixed gas, the second InAlNfilm is formed on the second wafer W.

Next, the second wafer W (second substrate) is unloaded from thereaction chamber 10 to the outside (S230).

Next, the function and effect of the vapor phase growth method accordingto the first embodiment will be described.

In the vapor phase growth of the InAlN film, unintentional galliumincorporation into the InAlN film becomes a problem. If the gallium isincorporated into the InAlN film, for example, a decrease in 2 DEGdensity and a decrease in electron mobility at the interface between theInAlN and the GaN occur. For this reason, for example, thecharacteristics of the HEMT using the stacked film of the GaN film andthe InAlN film deteriorate. In addition, an uncontrolled amount ofgallium is incorporated into the InAlN film, so that the reproducibilityof the characteristics of the HEMT is lost.

In particular, in a case where an InAlN film is continuously formed onthe GaN film, it is considered that substances containing galliumadhering to the wall surface or the like of the reaction chamber 10 atthe time of forming the GaN film is incorporated into the InAlN film. Asa method of suppressing unintentional gallium incorporation into theInAlN film, for example, it is considered effective to clean thereaction chamber before forming the InAlN film. However, if the reactionchamber is cleaned before forming the InAlN film, the throughput of thevapor phase growth apparatus greatly decreases.

In the vapor phase growth method according to the first embodiment, amixed gas is generated by mixing a group III element process gas and agroup V element process gas before being supplied to the reactionchamber 10. Then, the mixed gas is supplied into the reaction chamber 10to form a GaN film or an InAlN film on the wafer. Only one wafer is inthe reaction chamber 10. Then, in a state where one wafer self-rotatesat a high speed, the GaN film or the InAlN film is formed on the wafer.

According to the vapor phase growth method according to the firstembodiment, even in a case where the InAlN film is continuously formedon the GaN film, it is possible to suppress unintentional galliumincorporation into the InAlN film. According to the vapor phase growthmethod according to the first embodiment, a mixed gas of a group IIIelement process gas and a group V element process gas is generatedbefore being supplied to the reaction chamber 10, so that the occurrenceof a turbulent flow in the reaction chamber 10 is suppressed. For thisreason, it is considered that, for example, adhesion of substancescontaining gallium to the wall surface or the like of the reactionchamber 10 is suppressed during the formation of the GaN film. Inaddition, it is considered that, the occurrence of a turbulent flow inthe reaction chamber 10 is suppressed, and thus, the substancescontaining gallium adhering to the wall surface or the like of thereaction chamber 10 is suppressed from being desorbed into theatmosphere during the formation of the InAlN film.

In addition, it is considered that, the occurrence of a turbulent flowin the reaction chamber 10 is suppressed by the effect of the mixed gasbeing drawn by the wafer self-rotating at a high speed, and thus,adhesion of the substances containing gallium and detachment of thesubstances containing gallium to and from the wall surface or the likeof the reaction chamber 10 are suppressed. In addition, it is consideredthat, by self-rotating the wafer at a high speed, the reaction anddecomposition of the mixed gas can be restricted to the vicinity of thewafer surface, and thus, adhesion of the substances containing galliumto the wall surface or the like of the reaction chamber 10 issuppressed.

FIG. 3 is an explanatory diagram of the effects of the vapor phasegrowth method according to the first embodiment. By using the vaporphase growth method according to the first embodiment, the forming ofthe stacked film including the GaN film was performed 100 times or morewithout cleaning the reaction chamber 10. FIG. 3 illustrates thedepth-directional distribution of indium (In), aluminum (Al), gallium(Ga), and nitrogen (N) in the stacked film of the InAlN film and the GaNfilm formed without cleaning the reaction chamber 10.

FIG. 3 illustrates analysis results by Rutherford backscatteringspectroscopy (RBS). The horizontal axis is the depth based on thesurface of the InAlN film, and the vertical axis is the existence ratioof each element. For example, in the case of gallium, the ratiorepresented by Ga/(In+Al+Ga+N) is indicated by atom %.

The Gallium in the InAlN film was below the detection limit (6 atom %).The same sample was also analyzed by secondary ion mass spectrometry(SIMS), but the gallium in the InAlN film was 1,000 ppm or less.

Therefore, according to the vapor phase growth method according to thefirst embodiment, it is obvious that, even if the InAlN film is formedwithout interposing the washing of the reaction chamber 10 afterformation of the film containing gallium several times, thatunintentional gallium incorporation into the InAlN film does not occur.

In the vapor phase growth method according to the first embodiment, itis preferable that the rotation speed (first rotation speed) of thewafer at the time of forming the InAlN film is higher than the rotationspeed (second rotation speed) of the wafer at the time of forming theGaN film.

In a case where the InAlN film is used as a barrier layer of the HEMT,in stabilizing the characteristics of the HEMT, it is important toincrease the uniformity of the film thickness of the thin InAlN film andthe uniformity of the composition. The uniformity of the film thicknessand the uniformity of the composition become higher as the rotationspeed of the wafer is higher.

In a case where the GaN film is used as a channel layer of the HEMT,there is a concern that, as the amount of carbon incorporated into theGaN film increases, the 2 DEG concentration may decrease and theelectron mobility may decrease. Therefore, it is preferable that theamount of carbon in the GaN film is small. The carbon is incorporatedinto the GaN film from the TMG used for forming the GaN film.

The amount of carbon incorporated into the GaN film increases as therotation speed of the wafer increases. Therefore, from the viewpoint ofsuppressing the amount of carbon in the GaN film, it is preferable thatthe rotation speed of the wafer is low.

By setting the rotation speed (first rotation speed) of the wafer at thetime of forming the InAlN film to be higher than the rotation speed(second rotation speed) of the wafer at the time of forming the GaNfilm, the improvement of the uniformity of the film thickness of theInAlN film and uniformity of the composition and the suppression of theamount of carbon in the GaN film can be compatible with each other.

In addition, in a case where the InAlN film is used as a barrier layerof the HEMT and the GaN film is used as a channel layer of the HEMT, thethickness of the GaN film becomes larger than the thickness of the InAlNfilm. If film formation of a thick film is performed at a high rotationspeed, power consumption used for the film formation increases.Therefore, the production cost for the film formation is increased.Therefore, from the viewpoint of suppressing the production cost, it isalso preferable to set the rotation speed (first rotation speed) of thewafer at the time of forming the InAlN film to be higher than therotation speed (second rotation speed) of the wafer at the time offorming the GaN film. In other words, it is preferable to set therotation speed (second rotation speed) of the wafer at the time offorming the thick GaN film to be lower than the rotation speed (firstrotation speed) of the wafer at the time of forming the thin InAlN film.

It is preferable that the rotation speed (first rotation speed) of thewafer at the time of forming the InAlN film is 1,600 rpm or more and2,000 rpm or less. If the rotation speed is below the above-mentionedrange, there is a concern that the uniformity of the film thickness ofthe InAlN film and the uniformity of the composition may decrease. Ifthe rotation speed exceeds the above-mentioned range, it becomesdifficult to stably control the rotation speed.

It is preferable that the rotation speed (second rotation speed) of thewafer at the time of forming the GaN film is 500 rpm or more and 1,500rpm or less. If the rotation speed is below the above-mentioned range,there is a concern that the uniformity of the thickness of the GaN filmand the uniformity of the composition may decrease. If the rotationspeed exceeds the above-mentioned range, there is a concern that theamount of carbon incorporated into the GaN film becomes too large.

From the viewpoint of suppressing unintentional gallium incorporationinto the InAlN film, the first rotation speed and the second rotationspeed are preferably 300 rpm or more, more preferably 800 rpm or more,still more preferably 1,000 rpm or more.

As described above, according to the vapor phase growth method accordingto the first embodiment, it is possible to form an InAlN film in whichunintentional gallium incorporation is suppressed.

In addition, it is preferable that, after the indium aluminum nitridefilm is formed and the wafer W is unloaded from the reaction chamber 10,before the next wafer W is processed, deposits adhering to the holder 15are removed by gas phase etching in the reaction chamber 10.Alternatively, it is preferable to replace the holder 15 to whichdeposits have adhered with a new holder 15 or a holder 15 from whichdeposits have been removed outside the reaction chamber. By etching orreplacing the holder, it is possible to use a holder to which depositshave not adhered for each growth run, and thus, the initial state of theholder can be maintained to be the same state, so that the filmdeposition reproducibility is improved. The loading of the holder may beperformed at the same time when the wafer W to be processed next isloaded into the reaction chamber 10.

Second Embodiment

The vapor phase growth method according to the second embodiment issimilar to the first embodiment except that, after the first galliumnitride film is formed, before the first indium aluminum nitride film isformed, an aluminum nitride film or an aluminum gallium nitride film ofwhich thickness is smaller than the thickness of the first indiumaluminum nitride film is formed on the first substrate. Hereinafter, aportion of the redundant description of the first embodiment will beomitted.

FIG. 4 is a view illustrating process steps of the vapor phase growthmethod according to the second embodiment. Hereinafter, a case where analuminum nitride film is formed after formation of the first galliumnitride film before formation of the first indium aluminum nitride filmwill be described as an example.

The vapor phase growth method according to the second embodimentincludes a first substrate loading step (S100), a first GaN film formingstep (S110), a first AlN film forming step (S115), a first InAlN filmforming step (S120), a first substrate unloading step (S130), a secondsubstrate loading step (S200), a second GaN film forming step (S210), asecond AlN film forming step (S125), a second InAlN film forming step(S220), and a second substrate unloading step (S230).

The steps from the first substrate loading step (S100) to the first GaNfilm forming step (S110) are similar to those of the first embodiment.

Next, a first AlN film is formed on the first wafer W without unloadingthe first wafer W from the reaction chamber 10 (S115). The first AlNfilm is a single crystal. The thickness of the first AlN film is, forexample, 0.1 nm or more, preferably 0.3 nm or more and 5 nm or less. Thethickness of the first AlN film is smaller than the thickness of thefirst InAlN film.

At the time of forming the first AlN film, the first wafer W is rotatedat a predetermined rotation speed. The rotation speed is, for example,1,600 rpm or more and 2,000 rpm or less. In addition, the temperature ofthe first wafer W is, for example, 1,000° C. or more and 1,100° C. orless.

At the time of forming the first AlN film, for example, TMA usingnitrogen gas as a carrier gas is supplied from the first gas supply path11. In addition, ammonia is supplied from the second gas supply path 12.In addition, for example, nitrogen gas as a dilution gas is suppliedfrom the third gas supply path 13.

The TMA using nitrogen gas as a carrier gas, the ammonia, and thenitrogen gas are mixed to generate a mixed gas, and the mixed gas issupplied to the mixed gas chamber 21. The mixed gas is supplied from themixed gas chamber 21 through the shower plate 22 into the reactionchamber 10.

The mixed gas becomes a laminar flow in a direction substantiallyperpendicular to the surface of the first wafer W in the reactionchamber 10 and is supplied to the surface of the first wafer W. Themixed gas supplied to the surface of the first wafer W flows toward theouter periphery of the first wafer W along the surface of the rotatingfirst wafer W. By a chemical reaction of the mixed gas, a first AlN filmis formed on the first wafer W.

Next, a first InAlN film is formed on the first wafer W withoutunloading the first wafer W from the reaction chamber 10 (S120). Thefirst InAlN film forming step (S120) is similar to that of the firstembodiment.

Next, the first wafer W (first substrate) is unloaded from the reactionchamber 10 to the outside (S130).

Next, the second wafer W (second substrate) is loaded into the reactionchamber 10 (S200). The steps from the second substrate loading step(S200) to the second GaN film forming step (S120) are similar to thoseof the first embodiment.

Next, a second AlN film is formed on the second wafer W withoutunloading the second wafer W from the reaction chamber 10 (S215). Thesecond AlN film is a single crystal. The second AlN film is formed underthe process conditions similar to those of the first AlN film.

Next, a second InAlN film is formed on the second wafer W withoutunloading the second wafer W from the reaction chamber 10 (S220). Thesecond InAlN film forming step (S220) is similar to that of the firstembodiment.

Next, the second wafer W (second substrate) is unloaded from thereaction chamber 10 to the outside (S230).

Next, the function and effect of the vapor phase growth method accordingto the second embodiment will be described.

According to the vapor phase growth method according to the secondembodiment, similarly to the vapor phase growth method according to thefirst embodiment, it is possible to suppress unintentional galliumincorporation into the InAlN film.

In addition, similarly to the first embodiment, it is preferable that,after the indium aluminum nitride film is formed and the wafer W isunloaded from the reaction chamber 10, before the next wafer W isprocessed, the deposits adhering to the holder 15 are removed by vaporphase etching in the reaction chamber. Alternatively, it is preferableto replace the holder 15 to which the deposits have adhered with a newholder 15 or a holder 15 from which the deposits have been removedoutside the reaction chamber 10. The loading of the holder may beperformed at the same time when the wafer W to be processed next isloaded into the reaction chamber 10.

In a case where the InAlN film is used as a barrier layer of the HEMTand the GaN film is used as a channel layer of the HEMT, by interposinga thin AlN film or AlGaN film between the InAlN film and the GaN film,electron scattering is suppressed, and electron mobility is improved.Therefore, according to the vapor phase growth method according to thesecond embodiment, it is possible to form a stacked film suitable forapplication to the HEMT.

As described above, according to the vapor phase growth method accordingto the second embodiment, it is possible to form an InAlN film in whichunintentional gallium incorporation is suppressed. Furthermore, itbecomes possible to form a stacked film suitable for application to theHEMT.

EXAMPLE

After manufacturing the first sample by the vapor phase growth methodaccording to the first embodiment, the following procedure was repeatedeight times continuously, and thus, eight samples were manufactured. Nocleaning of the reaction chamber 10 is performed from the manufacturingof the first sample to the manufacturing of the eighth sample and duringthe manufacturing of the above eight samples.

While manufacturing the above 8 samples, in a state where the dummywafer was mounted on the holder 15, the inside of the reaction chamber10 was heated to remove substances adhering on the holder 15 after themanufacturing of each sample. After the holder 15 was unloaded from thereaction chamber 10, the 6-inch silicon wafer W was mounted on theholder 15, and the holder 15 and the wafer W were loaded into thereaction chamber 10.

Similarly to the second embodiment, after the AlN film and the AlGaNfilm as buffer layers were grown on the wafer W in the procedure similarto that of the second embodiment, a GaN channel layer, an AlN film(designed film thickness of 1 nm), an InAlN barrier layer (designed filmthickness of 10 nm) were grown. However, at the time of growing thebuffer layers, the channel layer, and the AlN film on the channel layer,a mixed gas of hydrogen and nitrogen was used as a carrier gas. Inaddition, at the time of growing the InAlN barrier layer, nitrogen gaswas used as a carrier gas.

Cloudiness of the surface was not observed in any of the eight wafersmanufactured in this manner, and it was confirmed that a high-qualityfilm was formed. For the eight wafers, the film thickness distributionof the InAlN in the radial direction (radii of 0, 20, 40, 60, and 70 mm)was evaluated by X-ray diffraction. The average value of the filmthickness of the InAlN film of each wafer was 10 nm±0.2 nm. The averagevalue for all the measurement points (40 points) of the eight wafers was9.89 nm, and the standard deviation was 0.2 nm.

Surface defects were evaluated for these eight wafers (SurfScan 6420produced by KLA-Tencor). Except for 5 mm around the wafer, the number ofdefects per wafer was 100 or less (defect size was 0.7 μm or more).

The above results indicate that a high-quality InAlN film is grown withgood reproducibility.

Heretofore, the embodiments of the invention have been described withreference to specific examples. The above-described embodiments aremerely provided as examples and do not limit the invention. In addition,the constituent elements of the embodiments may be appropriatelycombined.

In addition, in the embodiments, the case where the process gas is mixedbefore entering the mixed gas chamber 21 has been described as anexample, but the process gas may be configured so as to be mixed in themixed gas chamber 21.

In addition, in the embodiments, the case where two types of the heatersincluding the in-heater 24 and the out-heater 26 are provided has beendescribed as an example, but only one type of heater may be used.

In addition, although the reaction chamber for single wafer processingin which the substrates are processed one by one in the film formationhas been described as an example, the invention is also applicable to acase where a large number of wafers are mounted on a susceptor and afilm formation process is performed at the same time.

In the embodiments, descriptions of portions that are not directlyrequired for description of the invention, such as apparatusconfiguration and manufacturing method, are omitted, but necessaryapparatus configuration, manufacturing method, and the like can beappropriately selected and used. In addition, all the vapor phase growthmethods which are equipped with the elements of the invention and can beappropriately designed and changed by those skilled in the art areincluded in the scope of the invention. The scope of the invention isdefined by the claims and the scope of equivalents thereof.

1. A vapor phase growth method comprising: loading a first substrateinto a reaction chamber; generating a first mixed gas by mixing at leasta gallium containing gas and a nitrogen-compound containing gas; forminga first gallium-containing nitride film after the loading the firstsubstrate by supplying the first mixed gas from a shower plate providedabove the reaction chamber, a first surface of the first substrate andthe shower plate being separated by 3 cm or more, the first substratebeing rotated at a first rotation speed of 300 rpm or more; generating asecond mixed gas by mixing an indium containing gas, an aluminumcontaining gas, and a nitrogen compound containing gas; and forming afirst indium aluminum nitride film after the forming the firstgallium-containing nitride film by supplying the second mixed gas fromthe shower plate, the first substrate being rotated at a second rotationspeed of 300 rpm or more, and the forming the first indium aluminumnitride film being continuously conducted without unloading the firstsubstrate from the reaction chamber after the forming the firstgallium-containing nitride film.
 2. The vapor phase growth methodaccording to claim 1, wherein the reaction chamber is a reaction chamberfor single wafer processing, and a rotation of the first substrate isself-rotation.
 3. (canceled)
 4. The vapor phase growth method accordingto claim 1, wherein the second rotation speed is higher than the firstrotation speed.
 5. The vapor phase growth method according to claim 1,further comprising: forming an aluminum nitride film or an aluminumgallium nitride film having a thickness smaller than the thickness ofthe first indium aluminum nitride film after the forming the firstgallium-containing nitride film and before the forming the first indiumaluminum nitride.
 6. The vapor phase growth method according to claim 1,further comprising: unloading the first substrate from the reactionchamber after forming the first indium aluminum nitride film; loading asecond substrate into the reaction chamber without cleaning the reactionchamber; forming a second gallium-containing nitride film after theloading the second substrate by supplying the first mixed gas from theshower plate, the second substrate being rotated at the first rotationspeed; and forming a second indium aluminum nitride film after theforming the second gallium-containing nitride film by supplying thesecond mixed gas from the shower plate, the second substrate beingrotated at the second rotation speed.
 7. The vapor phase growth methodaccording to claim 1, wherein the nitrogen compound is ammonia.
 8. Thevapor phase growth method according to claim 1, wherein the firstsubstrate is a silicon substrate.
 9. The vapor phase growth methodaccording to claim 4, wherein the second rotation speed is 1,600 rpm ormore and the first rotation speed is 1,500 rpm or less.
 10. The vaporphase growth method according to claim 5, wherein the aluminum nitridefilm or the aluminum gallium nitride film has a film thickness of 0.1 nmor more and 5 nm or less.
 11. The vapor phase growth method according toclaim 1, wherein the shower plate includes a plurality of gas ejectionholes, and an interval between the gas ejection holes closest to eachother is 1 mm or more and 15 mm or less.
 12. The vapor phase growthmethod according to claim 1, wherein the shower plate has uneven portionon a gas ejection surface.
 13. The vapor phase growth method accordingto claim 12, wherein an angle between a surface of the uneven portionand a horizontal direction of the gas ejection surface is 45 degrees orless.